1. Field of the Invention
This invention relates generally to advanced oxidation processes, and more particularly to a method and apparatus for closed loop recycling of contaminated cleaning solutions by subjecting the contaminated cleaning solution to an ozone containing gas and alternating direct current and recycling the rinse water and cleaning solution dragged into said rinse water using a reverse osmosis means to separate the rinse water and reconcentrate the cleaning solution prior to returning them to the original cleaning process.
2. Brief Description of the Prior Art
Industrial cleaning processes are currently being re-evaluated and redesigned in order to minimize the amount of waste produced and the resulting cost of waste disposal. Waste disposal costs have soared in recent years, and there is increasing pressure from congress, and the public to reduce the amount and the toxicity of all industrial waste streams.
Aqueous cleaning formulations used in spray washers are frequently quoted as being environmentally safe and biodegradable. However, when they are exhausted and ready for disposal they will always contain the contaminates that were removed from the dirty parts. Automotive contaminates include motor oil, transmission fluid, benzene, lead, cadmium and the used cleaning solution often includes organic compounds from other cleaning processes that are dragged in on the parts which have been cleaned, such as carburetor cleaner. These compounds include phenol, benzene, creosols, xylenes, chlorinated hydrocarbons and various paint solvents. Most of these compounds are now on the EPA's new "TCLP` hazardous waste list. Waste cleaners frequently leach more than the limit of these organic compounds and are therefore considered to be hazardous wastes.
In the past, disposing of weak contaminated cleaners and replacing them with fresh cleaners has been the most cost-effective option. Replacing a cleaning bath requires shutting down the cleaning process, draining out the old cleaner, and filling the tank with the new cleaner. Then the old cleaner must be tested and disposed of properly. Testing and disposal costs have soared in recent years.
It would therefore be desirable to extend the useful life of cleaning solutions. Mechanical filters, oil skimmers and special oil releasing cleaning formulas are becoming quite common. None of these methods has eliminated the need for continued frequent disposal of used cleaning solutions. Solvent based cleaners can be distilled and reused. However, they tend to be flammable, sources of air pollution, odorous, or depleters of the ozone layer. There is a major shift underway from hazardous solvent based cleaners to aqueous based cleaning products.
Products are commercially available to separate oils and greases from cleaning solutions to help increase the life of the cleaning bath. However, these products do not eliminate the eventual need for disposal of the contaminated oil or the spent cleaning solution. Some facilities have switched to very expensive burn-off ovens to burn off the oils and greases, followed by dry shot blasting. This method is extremely energy intensive and costly, and is not usable on plastic or aluminum.
Industries which generate waste must determine if their used cleaning wastes are hazardous before disposing of them. A complete lab analysis of just one waste stream can cost from $2,000 to $3,000.00 and disposal costs for hazardous waste vary from $300.00 to $1,200.00 per barrel. Even when the waste has been properly disposed of, the waste generator remains forever liable for any future problems caused by the waste.
The U.S. Environmental Protection Agency (EPA) now requires hazardous waste generators to certify on their hazardous waste manifests that the amount of hazardous waste produced has been minimized prior to shipping the waste. One current method is to boil the water off and ship the solids. This is one of the most energy intensive and costly methods available. Systems that boil 50 gallons/day can cost over $10,00.00 to purchase. They tend to scale easily, thus, reducing their energy efficiency and they do not solve the problem of solids disposal.
Another disposal option is to set up and man a small scale waste water treatment and neutralization system. This option requires trained operators, more chemicals, the energy required to pump and filter the solution prior to discharge, and a permit to discharge the treated waste water. These systems also produce large volumes of wet sludge requiring further treatment prior to disposal.
Chlorinated solvents are rapidly being phased out and replaced by aqueous cleaners in order to avoid the new ozone-depletion product-labeling law. This new law requires manufactures to label products which have been cleaned with ozone depleting chemicals as having been manufactured with an ozone depleting chemical. These solvents are being heavily taxed and considering waste disposal costs and cradle to grave liability issues, they are no longer cost effective. These market forces are driving industry to replace solvent cleaners with aqueous cleaners.
The following U.S. Patents and publications are discussed as further background and also as an information disclosure reviewing past attempts to solve the problems outlined above.
U.S. Pat. Nos. 3,149,906 and 4,212,330 discloses methods for treating animal fibers with gaseous ozone and steam wherein the ozone and steam mixture is used to shrink-proof proteinous animal fibers.
U.S. Pat. No. 5,097,556 discloses a laundry waste water treatment and wash process using only ozone as the bleaching and disinfecting means and excludes the use of any cleaning additives to the wash water other than ozone. The washing and ozone treatment are both ambient temperature processes and pertain to bleaching and disinfecting of laundry with detergent free rinse water. The rinse water is recycled using ozone and course mechanical filters. The bleaching and disinfecting is accomplished by rinsing with cold water containing ozone.
U.S. Pat. No. 4,220,529 discloses a process for the direct purification of cyanide contaminated rinse water by combining hydrogen peroxide and sodium hypochlorite to produce singlet oxygen in the contaminated rinse water.
U.S. Pat. No. 3,546,114 discloses a process for ozonation of industrial waste water at temperatures above 160.degree. F. to sterilize the waste rinse water before reuse in rinsing new food containers and prior to packaging food in the rinsed containers.
U.S. Pat. No. 4,076,617 discloses a process for purifying waste material using a combination of ozone and ultrasonics.
U.S. Pat. Nos.: 3,746,756; 4,242,309; 4,185,025; 5,015,760; 5,103,061; 3,862,142; 4,404,110; 3,658,667; 3,637,721; and 4,181,652; all relate to chemically manufacturing very specific compounds by reacting other very specific raw material compounds with ozone under very specific conditions. None of them suggest producing a reusable cleaning solution out of the contaminates dragged into the cleaning solution.
All of the references listed above related to either purifying waste water or to producing a completely different product, and none combine ozone and electrolytic treatment of a material.
In an article published in Ozone Science and Engineering, Vol. 12, Num. 2, 1990, p. 115-131, titled "Decomposition of Ethylene Glycol by the Combined Use of Ozone Oxidation and Electrolytic Methods", researchers Takahashi and Katshuki examined the rates of oxidation of ethylene glycol using ozone, electrolysis, and the combination of ozone and electrolysis simultaneously. Their research indicated that the reaction mechanism was different in all three cases since the reaction products were all different.
The present invention is distinguished over the prior art in general, and these patents in particular by an advanced oxidation process and apparatus for closed loop treating and recycling of cleaning solutions contaminated with used surfactants, fats, oils, greases, and inorganic and organic contaminates which converts the contaminated cleaning solution into a reusable cleaning solution containing useful polar water soluble surfactants, detergents, wetting agents and emulsifiers. The contaminated cleaning solution is subjected to an ozone containing gas and alternating direct current. The reaction with ozone containing gas is carried out in a mixed vapor (gas/liquid mist) state. Fats, oils, greases and organic contaminates are converted into useful polar water soluble surfactants, detergents, wetting agents and emulsifiers and the excess organic surfactants, detergents, wetting agents, and emulsifiers are simultaneously converted into carbon dioxide, nitrogen, and water. The treated cleaning solution is reused as the cleaning solution in the original cleaning process from which the contaminated cleaner was obtained. The rinse water in the cleaning process becomes contaminated with dilute reused cleaning solution and is recycled by reverse osmosis to separate the rinse water and reconcentrate the cleaning solution. The reconcentrated cleaning solution is returned to the original cleaning process for reuse and the reverse osmosis product water is returned to the original rinse station for reuse.
The present process permits the continued use of a cleaning solution long after it would have been dumped using previously known methods. Since the organic soils are converted from contaminates to cleaning compounds the need for frequent bath dumps is totally eliminated. Because oil and grease do not accumulate in the treated cleaning solution reverse osmosis may be used to recover and recycle the cleaner and rinse water from the cleaning process rinse water. The amount of water and chemicals needed to maintain the cleaning process is substantially reduced, and the cost of waste disposal is eliminated. The present process also allows the cleaning bath to be maintained at the peak performance of a new bath resulting in decreased cycle times and decreased energy consumption needed to clean the parts. This results in a more efficient and cost effective cleaning process.